#include "drake/examples/multibody/cylinder_with_multicontact/populate_cylinder_plant.h"

#include "drake/multibody/tree/uniform_gravity_field_element.h"

namespace drake {
namespace examples {
namespace multibody {
namespace cylinder_with_multicontact {

using drake::multibody::CoulombFriction;
using drake::multibody::MultibodyPlant;
using drake::multibody::RigidBody;
using drake::multibody::SpatialInertia;
using drake::multibody::UnitInertia;
using Eigen::Vector3d;
using geometry::Cylinder;
using geometry::HalfSpace;
using geometry::Sphere;
using math::RigidTransformd;

namespace {
void AddCylinderWithMultiContact(
    MultibodyPlant<double>* plant, const RigidBody<double>& body,
    double radius, double length, const CoulombFriction<double>& friction,
    double contact_spheres_radius, int num_contacts) {
  const Vector4<double> orange(1.0, 0.55, 0.0, 1.0);
  const Vector4<double> red(1.0, 0.0, 0.0, 1.0);

  // Visual for the Cylinder
  plant->RegisterVisualGeometry(
      body,
      /* Pose X_BG of the geometry frame G in the cylinder body frame B. */
      RigidTransformd::Identity(), Cylinder(radius, length), "visual", orange);

  // Add a bunch of little spheres to simulate "multi-contact".
  for (int i = 0; i < num_contacts; ++i) {
    const double theta = 2.0 * i / num_contacts * M_PI;
    const double x = cos(theta) * radius;
    const double y = sin(theta) * radius;
    // Top spheres:
    /* Pose X_BG of the geometry frame G in the cylinder body frame B. */
    const RigidTransformd X_BS1(Vector3d(x, y, length / 2));
    plant->RegisterCollisionGeometry(
        body, X_BS1, Sphere(contact_spheres_radius),
        "collision_top_" + std::to_string(i), friction);
    plant->RegisterVisualGeometry(body, X_BS1, Sphere(contact_spheres_radius),
                                  "visual_top_" + std::to_string(i), red);

    // Bottom spheres:
    const RigidTransformd X_BS2(Vector3d(x, y, -length / 2));
    plant->RegisterCollisionGeometry(
        body, X_BS2, Sphere(contact_spheres_radius),
        "collision_bottom_" + std::to_string(i), friction);
    plant->RegisterVisualGeometry(body, X_BS2, Sphere(contact_spheres_radius),
                                  "visual_bottom_" + std::to_string(i), red);
  }
}
}  // namespace

void PopulateCylinderPlant(double radius, double length, double mass,
                           const CoulombFriction<double>& surface_friction,
                           const Vector3<double>& gravity_W,
                           MultibodyPlant<double>* plant) {
  const SpatialInertia<double> M_Bcm =
      SpatialInertia<double>::SolidCylinderWithMass(
          mass, radius, length, Vector3<double>::UnitZ());
  const RigidBody<double>& cylinder = plant->AddRigidBody("Cylinder", M_Bcm);

  // The radius of the small spheres used to emulate multicontact.
  const double contact_radius = radius / 20.0;

  // The number of small spheres places at each rim of the cylinder to emulate
  // multicontact.
  const int num_contact_spheres = 10;

  // Add geometry to the cylinder for both contact and visualization.
  AddCylinderWithMultiContact(
      plant,
      cylinder, radius, length, surface_friction,
      contact_radius, num_contact_spheres);

  // Add a model for the ground.
  Vector3<double> normal_W(0, 0, 1);
  Vector3<double> point_W(0, 0, 0);

  // A half-space for the ground geometry.
  RigidTransformd X_WG(HalfSpace::MakePose(normal_W, point_W));
  plant->RegisterCollisionGeometry(plant->world_body(), X_WG, HalfSpace(),
                                   "collision", surface_friction);

  // Add visual for the ground.
  plant->RegisterVisualGeometry(
      plant->world_body(), X_WG, HalfSpace(), "visual");

  plant->mutable_gravity_field().set_gravity_vector(gravity_W);
}

}  // namespace cylinder_with_multicontact
}  // namespace multibody
}  // namespace examples
}  // namespace drake
